1. Field of the Invention
The invention relates to a method of radiographic inspection of wooden members and more particularly to the use of a radiopaque penetrant in the member inspected to visually enhance the contrast of the image of any internal defects with the image of other properties therein on a radiographic film.
2. Description of the Prior Art
Radiopaque penetrants have been used to improve the contrast of radiographic film image of defects in materials of substantially uniform density and internal formation such as bronze, brass, other metals, plastic and rubber. Even in these relatively homogeneous materials, the use of known penetrants may be restricted because of their extremely low toxicity threshold limit value (TLV). For instance, s-tetrabromoethane (C.sub.2 H.sub.2 Br.sub.4), a commercially available penetrant, has a toxicity TLV of only one part per million, making it extremely hazardous to use for radiographic purposes. Another radiopaque penetrant, a solution of zinc iodide crystals (ZnI.sub.2) in water and isopropyl alcohol, poses little health problem, but its use may lead to contamination of the member inspected by local staining and discoloration caused by residual ZnI.sub.2 crystals.